This invention relates to automated processing of material for rejecting undesired constituents of the material and, more particularly, to segregating shell fragments from nut meats for rejecting the shell fragments during the automated processing of food nuts. Specifically, the invention is directed to bandpass filtering the signal produced by a transducer connected to a target plate against which particles, such as nut meats and shell fragments, are impacted for improved discrimination between shell fragments and nut meats, as well as solving the mass weight problem so that signals within the frequency pass and which are typically associated with shell fragments nut which exceed a predetermined amplitude are considered to be produced by nut meats such that these nut meats are not rejected.
There are various situations in which one component of bulk material is desirably separated from another component or components of the material. One situation where such a need arises is in the field of processing foodstuffs, particularly when large quantities of edible product are harvested or otherwise being processed. For example, Armstrong et al., U.S. Pat. No. 3,004,662, and Baigent, U.S. Pat. No. 3,127,016, disclose sorting foreign substances from foodstuffs; Cragg, U.S. Pat. No. 3,559,805, discloses removing stones and rocks from harvested potatoes; and Girodat, U.S. Pat. No. 3,675,660, discloses rejecting relatively hard objects, such as rocks, large enough to damage the elevator, cylinder, or concave of a combine harvester during the harvesting of crop material.
Generally, these patents are directed to culling inorganic material from foodstuffs at an early stage during the processing of the foodstuff. The inorganic material and the foodstuff have substantially different characteristics of mass and density, which can facilitate the discrimination between the unwanted material and the foodstuff.
Each of the referenced patents discloses a structure which comes into contact with a material to be processed. The structure is connected to a transducer. One component of the material causes the transducer to produce a signal having a first characteristic, and another component of the material causes the transducer to produce a signal having a second characteristic. Generally, a high pass filter is used to discriminate one component of the material from the other, and the amplitude produced by the passed signal is detected by a threshold detector which controls the operation of a reject device.
The discrimination between unwanted and desired components of bulk material is also present at later stages of processing foodstuffs. The problems which attend separation of unwanted and wanted components of the material at these later processing stages is exacerbated by several factors. One factor is that the characteristics of the unwanted material and the characteristics of the wanted material lessen, which renders discrimination between the undesired and desired components difficult. For example, the segregation can be between two components of organic material, rather than between an inorganic component and an organic component. Furthermore, the processing of the foodstuff can contribute to reducing the differences between the physical characteristics of the undesired and desired components of the material, for example, differences in the mass and density of the components of the material are reduced.
One situation where problems have arisen is during the processing of food nuts where shells and shell fragments are desirably culled from shelled nuts before the nut meats are packaged. The reasons for culling shells and shell fragments from nut meats are to avoid the risk of injury to a consumer who might otherwise inadvertently chew or swallow a shell and also to avoid customer dissatisfaction by minimizing the amount of unedible shells in packages of shelled nuts for which the consumer has paid.
Various techniques for culling shell fragments from nut meats are known. Originally, separation was performed by hand.
Rising labor costs and advances in technology have subsequently led to automated techniques for rejecting shell fragments from nut meats. One known technique used for sorting shell fragments from nut meats uses ultraviolet light for color sorting. The ultraviolet absorption characteristics of shell fragments differ from the ultraviolet absorption characteristics of nut meats. One such color sorter is the Model 5141E Color Sorter manufactured by Scan-Core, Inc. located in Mountain View, Calif.
Another automated technique for discriminating between shell fragments and nut meats is disclosed in Parker et al., U.S. Pat. No. 4,212,398. Parker et al., U.S. Pat. No. 4,212,398, discloses a technique which is based on differentiation of the characteristic frequencies of the signal produced by a transducer connected to a sounding plate upon impact of shell fragments, on the one hand, and nut meats, on the other.
Shell fragments generally cause the transducer to produce a signal having one frequency characteristic, whereas nut meats cause the transducer to produce a signal having a different frequency characteristic. Unfortunately, the circuit disclosed in Parker et al., U.S. Pat. No. 4,212,398, includes a high pass filter which has a frequency response characteristic that does not provide sufficient selectivity. The use of a high pass filter is adequate to separate stones from nuts during early stages of processing, but does not possess sufficient selectivity to adequately separate shells and shell fragments from nut meats during later processing stages after shelling.
Furthermore, Parker et al., U.S. Pat. No. 4,212,398, does not address the mass weight problem. Specifically, although the general circumstance is that shell fragments produce a signal having a different frequency from the frequency of the signal produced by nut meats, nevertheless, some nut meats, because they are dry, for example, cause the transducer connected to the sounding plate to produce a signal having a frequency characteristic similar to the frequency characteristic produced by a shell fragment upon impact with the sounding plate. The circuit disclosed in Parker et al., U.S. Pat. No. 4,212,398, is not able to discriminate between such nut meats and shell fragments. After amplifying the input signal and filtering low frequency signals from it, a comparator included in the circuit disclosed in Parker et al., U.S. Pat. No. 4,212,398, converts those original oscillations which exceed a predetermined threshold amplitude into voltage pulses that are counted in a counter. If the count exceeds a minimum set into the counter, the counter produces a signal. This signal initiates an output signal of predetermined duration, which after undergoing a delay, operates an air valve that is connected with an air nozzle located along a rebound trajectory, so that an air blast deflects the particle into a reject trajectory. Furthermore, oscillations in the input signal that exceed another and higher threshold amplitude can be converted into pulses which themselves initiate the output signal without being counted. In this instance the signal that is produced overrides the output signal derived from the counter and is of longer duration, which produces a longer air blast, so that heavy particles are deflected. Unfortunately, many of these heavy particles prove to be large nut meats. Consequently, nut meats are rejected along with shell fragments with attendant economic loss.